Roles of NEIL3 DNA glycosylase in telomere dynamics and DNA demethylation in glioblastoma: From molecular insights topreclinical target validation

There is no cure for glioblastoma (GBM), the most lethal primary brain tumor. Cancer cells must activate mechanisms to maintaining telomeres, the physical ends of our chromosomes, in order to acquire limitless replicative potential. While mostcancers display telomerase reactivation (TEL(+)), others rely on a DNA recombination-based mechanism called ALT. Although targeting DNA repair and telomere maintenance mechanisms have emerged as important therapeutic strategies for many cancers, identifying suitable targets for such strategies in GBM remains a considerable challenge.Telomeres need special protection from oxidative guanine damage – an inevitable consequence of cellular metabolism. Involved in the removal of oxidized guanines is the DNA repair protein NEIL3, a DNA glycosylase recruited to telomeres by the shelterin component TRF1. Notably, like other members of its protein family, NEIL3 has been proposed to participate in the oxidative demethylation pathway that mediates gene-specific removal of 5-methylcytosine in DNA, an epigenetic mark with profound impact on gene expression. However, the underlying mechanisms of this pathway and its relevance to cancer remain unknown. We have obtained evidence that NEIL3 is a relevant target to eradicate GBM cells. Specifically, NEIL3 is upregulated in GBM tumors and promotes chemoresistance in GBM in vitro. In addition, RNAi-mediated depletion of NEIL3 in TEL(+) cellselicits telomere erosion and activation of a DNA damage response. Notably, our results have revealed that the expression of a crucial telomere protection factor is modulated by NEIL3 at the transcriptional level. As a step to promote precision medicine in adult and pediatric GBM, this proposal aims to understand the mechanisms whereby NEIL3 regulates telomeredynamics, not only in TEL(+) cells but also in ALT cells where we predict a special requirement for NEIL3. It also aims to evaluate the importance of NEIL3 in DNA demethylation in relation to cancer, and test its potential as a therapeutic target inglioblastoma.In the short term, our results will provide new insights into telomere repair and maintenance mechanisms in TEL(+) and ALT cells, as well as the mechanisms regulating DNA (de)methylation in cancer, revealing cancer-relevant networks controlled by NEIL3. In the longer-term, our experiments could pave the way for novel DNA repair-based or epigenetic strategies against cancer. As telomeres play a central role in aging, our research may also have implications for aging-associated disorders.